New light sources, such as an LED and an organic EL, have been recently increasing their demands as elements for illumination or display taking advantages of low power consumption and long life. Particularly, an LED has been used in various fields of electrical and electronic appliances, such as a mobile communication device like a cellular phone, etc., a display, an automobile instrument panel, a signal, and other home appliances. In such electrical and electronic appliances miniaturization is progressing more and more from the demand for better design, portability, etc. As a key technology for realizing such miniaturization, surface-mount technology (SMT) has gained popularity, and been utilized in many electrical and electronic appliances. According to the technology, the packaging density of an electronic substrate can be increased dramatically and such miniaturization as has been unattainable can now be realized.
For a manufacturing process applying the SMT, since the entire parts mounted on an electronic substrate are heated for soldering, only a material that is resistant to the soldering temperature (approximately 240° C.) can be used. Meanwhile, a trend toward a lead-free solder is going on recently from the environmental concern, and use of a tin-silver alloy, etc. has been started. The melting points of such lead-free solders are higher than those of conventional lead solders, and therefore the soldering temperature is getting higher (approximately 260° C.). An LED is no exception, and the heat resistance enduring the SMT is required. An LED module is generally constituted of a light emitting semiconductor part, a lead wire, a reflector functioning also as a housing, and a transparent sealant sealing the semiconductor, which are mounted onto a circuit pattern on a substrate with a conductive adhesive, a solder, etc. to an LED element and connected by wire bonding. Concerning the reflector part to be provided at the circumference of the LED element in order to increase the light utilization rate of the LED, products using a material such as a ceramic or a heat-resistant plastic have been commercialized. Since a ceramic has a productivity problem, an LED reflector using a resin, such as a heat-resistant plastic has been drawing attention.
A problem of the resin-made LED reflector is decrease in the light reflectance caused by discoloration of the resin due to heating or heat history during a manufacturing process of the LED module or under an actual application environment. For example, such heating takes place, as, in an injection molding step, 300 to 350° C. for several minutes; in a thermal curing step of a conductive adhesive or a sealant, 100 to 200° C. for several hours; and in a soldering step, in a case a lead-free solder (a tin-silver-copper alloy solder, etc.) is used according to SMT, a peak temperature of 260° C. or higher for several minutes. Since the light reflectance of an LED reflector has large influence on the light extraction efficiency, decrease in the light reflectance by 1 percentage point only cannot be neglected.
Further, since an LED reflector is generally a finely and complicatedly formed molded part in a size of about 1 to 2 mm, the material thereof requires good fabricability enabling reproduction of a desired form by injection molding, etc. Additionally, since the light reflectance may be deteriorated even by slight deformation of an LED reflector, the material therefor is required to be superior in mechanical strength and dimensional stability. Further, since it is occasionally exposed to high temperatures as described above, good heat resistance is also required. Meanwhile, such physical properties are also required with respect to a reflector for a light emitting apparatus other than an LED reflector.
Concerning a material for molding an LED reflector, various studies have been already conducted. For example, Patent Literature 1 listed below proposes a resin composition prepared by adding a glass fiber, and additionally titanium oxide according to need, to a melt processable polyester, such as an aromatic polyester and an aromatic polyester amide. Patent Literature 2 listed below proposes a resin composition for a reflective plate, prepared by adding a potassium titanate fiber and wollastonite to a semiaromatic polyamide, whose aromatic monomer content based on the total monomer components is 20 mol-% or more. Patent Literature 3 listed below proposes a material for a reflective plate for a UV ray emitting source composed of a thermoplastic resin and a compound containing a potassium titanate as an inorganic compound which can reflect visible light as well as UV rays. Patent Literature 4 listed below proposes a polyamide resin composition for molding an LED reflector, prepared by adding titanium oxide, and magnesium hydroxide to a certain polyamide resin. Patent Literature 5 listed below proposes a technology for manufacturing an LED reflector by injection-molding a resin composition containing a wholly aromatic thermotropic liquid-crystal polyester having good heat resistance and a white pigment.
Recently, owing to an invention of a white LED, its market has been growing rapidly in applications such as a liquid-crystal display panel and illumination. Concerning a white LED, there is currently no single light source type, and various types with combined light sources are known. For example, a type combining a plurality of LEDs, which can reproduce RGB colors, such as red (R; 630 nm), green (G; 525 nm), and blue (B; 470 nm), to synthesize a white color, and a type utilizing a wavelength conversion action by adding a fluorescent substance into a sealing resin, are known. As an LED utilizing a wavelength conversion, a type using as a light source an LED emitting near-ultraviolet to ultraviolet rays, which have a shorter wavelength than a conventional LED, is known (e.g. see Patent Literature 6). For such a reflector for a white LED, from a viewpoint of improvement of the brightness, high light reflectance not only for the vicinity of an average wavelength of 470 nm equivalent to the wavelength of a blue LED, but also for a shorter wavelength down to about 420 nm is required.